Fish that leap into passing boats may be a fisherman’s fantasy, but
scientists fear that hyperactive Asian carp will reach the U.S. Great
Lakes, devour the base of the food chain and spoil drinking water for
40 million people.

In less than a decade since escaping southern
U.S. fish farms, the hardy and voracious carp have come to dominate
sections of the Mississippi River and its tributaries.

"It is a
crisis," said Phil Moy of the University of Wisconsin and the
government-affiliated water protection group Sea Grant. "We’ve seen
some pretty significant adverse invaders in the Great Lakes. Right now,
it’s the carp, but what’s around the corner?"

The leaping fish
are silver carp that jump haphazardly when alarmed by passing boats and
have injured boaters, some of whom have taken up garbage can lids as
shields.

The only barriers between dense populations of silver
and bighead carp — two closely related Asian carp species — and the
world’s largest collective body of fresh water are a few miles (kms) of
waterway and a little-tested underwater electrical field spanning a
canal near Chicago.

The idea of adding a few more varieties of
fish to the Great Lakes — which have been abused by polluters,
overfished, invaded by scores of unwanted species and repopulated with
nonnative fish to eat invaders and please anglers — would not appear
catastrophic in light of the range of global environmental crises.

But
scientists believe the carp, which escaped lagoons in Arkansas during
late 1990s flooding, could set off an ecological collapse in the lakes,
ruining the primarily recreational $5 billion fishery and posing a
threat to water quality for millions of people.

"With invasive
pest species, we can’t turn back the clock, the lakes will be altered
for good," said Cameron Davis of the group Alliance for the Great
Lakes. "Not only do invasive species unravel the food web they also
fool public perception: The lakes look cleaner because the food has
been stripped out."

Carp that can grow to 100 pounds (45 kg)
filter huge amounts of water, consuming 40 percent of their body weight
per day in microscopic plant and animal life that form the foundation
of the aquatic food chain. The loss of this food relied on by crayfish
and smaller fish such as alewifes, sculpins and perch would in turn
eliminate the prey for popular game fish such as salmon, trout and bass.

By Andrew Stern